Harmonic noise suppression in electromagnetic flowmeter

Details Harmonic noise suppression in electromagnetic flowmeter Harmonic noise suppression in electromagnetic flowmeter

1978-12-07

1980-10-14

Ruehl, Charles A.

Measuring and testing

Volume or rate of flow

By measuring electrical or magnetic properties

G01F 160

Patent

active

042274087

ABSTRACT:
An electromagnetic flowmeter in which fluid to be metered passes through a flow tube to intersect a magnetic field whereby the voltage induced in the field is transferred to a pair of electrodes mounted in the flow tube to yield a flow-induced signal. This field is established by an electromagnet supplied with excitation current through a periodically-operated switch to create a magnetic field which during each operating cycle is alternately turned on and off or reversed in flux direction at a predetermined drive frequency, as a consequence of which the signal includes undesirable noise components formed by even and odd harmonics of the drive frequency. To suppress such harmonic noise, the flow-induced signal is applied to a converter that includes a pair of synchronous demodulators operating in phase opposition and so synchronized with the periodically-operated switch that one demodulator passes its output to an integrator during the first half cycle of the drive frequency only in a gating interval in which the magnetic field is turned on and is at a constant flux level, and the other demodulator thereafter passes its output to the same integrator during the second half cycle only in a gating interval in which the magnetic field is turned off or is at a constant flux level in the reverse direction.

REFERENCES:
patent: 3783687 (1974-01-01), Mannherz et al.
patent: 4159645 (1979-07-01), Cushing

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